Cook squeezes one end of rubber stopper (5)
I believe the answer is:
brake
'stopper' is the definition.
(I've seen this before)
'cook squeezes one end of rubber' is the wordplay.
'cook' becomes 'bake' (baking is a kind of cooking**).
'squeezes' indicates putting letters inside (squeeze can mean hug or embrace).
'one end of' indicates one should take the final letters.
The final letter of 'rubber' is 'r'.
'bake' placed around 'r' is 'BRAKE'.
(Other definitions for brake that I've seen before include "Constraint" , "Horse-drawn carriage" , "Device for slowing vehicle" , "Stop or slow car" , "Device for slowing or stopping car" .)